It has become common when using a cellular handset or smart-phone to have the capability to accurately locate the position of the cellular device. Positioning is required during a 911 emergency call, and for the use of location-aware software applications (LASA), e.g. navigation and location-targeted advertising. Cellular location technologies use one or more of a variety of methods, including Uplink-Time Difference of Arrival (U-TDOA) for GSM networks, Advanced Forward Link Trilateration (AFLT) for CDMA networks, and handset-based Global Positioning System (GPS) or Assisted GPS (A-GPS) in any type of cellular network to determine the location of the handset.
The number of indoor repeater applications has increased greatly in the last several years (and should continue to expand unabated), but today's public safety sensitive environment has highlighted a shortcoming of these designs. Although the increased indoor wireless coverage has proved to be a boon for the wireless customer from both a value of service and safety standpoint, recent gains in location services for both navigation and public safety have left indoor applications as position location holes.
In indoor applications, the normal methods used for location determination (i.e. direct reception of GPS by the mobile station or triangulation using the signals from multiple base stations) do not work. Signals from the GPS system are sufficiently weak that even if the mobile station's GPS receiver might ultimately be able to lock on to the satellites, the acquisition time will be too long. Furthermore, indoor service is typically provided either by a single strong local cell, distributed within the building, or by using a repeater, so there are not multiple signals on which to triangulate. Repeaters tend to exacerbate the problem due to inherent delays which facilitate erroneous triangulation coordinates, in addition, repeater signals are significantly stronger than macro network leakage signals, thus reducing the capability of receiving macro position signals.